1. Field of the Invention
Embodiments of the present invention relate to methods and apparatus for handling tubulars using top drive systems. Particularly, the invention relates to methods and apparatus for engaging and disengaging a tubular handling apparatus from a tubular. More particularly still, the invention relates to a release mechanism for preventing the gripping elements of a tubular handling apparatus from locking during operations.
2. Description of the Related Art
It is known in the industry to use top drive systems to rotate a drill string to form a borehole. Top drive systems are equipped with a motor to provide torque for rotating the drilling string. The quill of the top drive is typically threadedly connected to an upper end of the drill pipe in order to transmit torque to the drill pipe. Top drives may also be used in a drilling with casing operation to rotate the casing.
In order to drill with casing, most existing top drives require a threaded crossover adapter to connect to the casing. This is because the quill of the top drives is not sized to connect with the threads of the casing. The crossover adapter is design to alleviate this problem. Typically, one end of the crossover adapter is designed to connect with the quill, while the other end is designed to connect with the casing.
In some instances, a tubular handling apparatus having movable gripping elements can be connected below the top drive to grip a tubular, such as casing, so that the tubular handling apparatus and the tubular may be driven axially or rotationally by the top drive. The tubular handling apparatus may be referred to as internal or external gripping tools depending on whether the tool grips an internal or external surface of the tubular.
Some of the tubular handling apparatus may use wedge type slips to grip the tubular. In the case of an internal gripping tool, the wedge slips are moved downward along a mating wedge surface to urge the wedge slips radially outward into contact with the interior surface of the tubular. To increase the gripping force on the tubular, the wedge slips may be provided with teeth on the gripping surface. Generally, the teeth are arranged to point up in order to prevent the tubular from sliding down. This arrangement allows the teeth to “bite” into the tubular in response to the weight of the tubular.
There is a need, therefore, for methods and apparatus for ensuring effective release of the wedge slips from the tubular.